Maternal FT4 Associated With Fetal Growth Trajectories in Prospective Cohort

Researchers analysed 69,675 singleton pregnancies in a prospective cohort, measuring maternal FT4, thyroid-stimulating hormone and thyroid peroxidase antibodies in the first or second trimester. They assessed fetal growth using 324,886 ultrasound observations from 13 to 41 weeks’ gestation, covering head and abdominal circumference, femur length, biparietal diameter and estimated fetal weight. Models evaluated growth velocities and defined growth-restriction patterns using population-based 10th percentiles.

Higher FT4 was associated with modestly faster growth across the measured parameters. The estimated difference in fetal-weight growth velocity between the 10th and 90th FT4 percentiles was 3.07 g/week (95% CI 2.88–3.26). Hypothyroxinemia was associated with slower velocities across parameters and higher odds of symmetrical growth restriction (OR 1.76, 95% CI 1.37–2.26). The authors also reported that some associations varied by TPO antibody status.

This observational study identifies associations, not evidence that changing thyroid hormone levels would alter fetal growth. The authors noted that the clinical relevance of the differences requires further investigation. The study was supported by Chinese public and institutional funding; the authors declared no competing interests.